The invention relates to an improved procedure for the removal of initiators from graft products, in which the grafting was initiated by means of cerium(IV) salts.
The grafting of unsaturated compounds onto basic supports containing hydroxyl groups, as is disclosed in DE 38 11 042 and DE 43 10 964 and the publications EP 0 337 144 and EP 0 565 978 corresponding to these, is based on the procedure of Mino and Kaizermann (1958). Here, the grafting is initiated by cerium(IV) salts.
Washing of the graft product with 0.5 M sulfuric acid, as well as washing with acidic sodium sulfite solution (0.25 M solution of sodium sulfite in 0.25 M sulfuric acid), is known for the removal of cerium salts from the graft product. This process, however, in many cases has to be repeated a number of times in order to remove the cerium salts adequately from the product. It is seen that for cation exchangers, e.g. graft polymers based on acrylamidomethylpropanesulfonic acid, this procedure is inadequate. Working with acidic sulfite solution is disadvantageous for reasons of safety in the workplace. For other graft polymers which, for example, contain epoxy groups, repeated washing with the strong mineral acid is disadvantageous because a marked proportion of the epoxy groups are hydrolyzed here, or because the sulfite ions react with the epoxy groups. On account of this, in some graft products, in particular those which contain epoxy groups, a measurable residue (typically about 200 ppm of cerium) of cerium salts still remains in the product. In particular, if the separating materials prepared by means of grafting are used in biotechnology or for the preparation of pharmaceutical products, removal of cerium salts to below the detection limit of atomic absorption spectroscopy (10 ppm) is an essential property.
The object is thus to remove cerium salts from graft products which have been obtained by means of cerium(IV) initiation so that fewer than 100 ppm of cerium remain in the product.
It has been found that cerium salts can be removed more completely from the graft products if a mineral acid solution of ascorbic acid is used for washing.
The invention relates to procedures for the removal of initiators from graft products, in which the grafting was initiated by means of cerium(IV) salts, by washing with a mineral acid solution, ascorbic acid being added to this solution.
Apart from in the publications already mentioned, separating materials based on graft polymers in which the grafting is initiated using cerium(IV) salts are disclosed in a number of further publications: EP 0 697 905, EP 0 708 919, EP 0 721 372, EP 0 722 360, EP 0 722 361, EP 0 722 362, EP 0 789 620 and PCT/EP 98/01 880.
According to the invention, the separating materials from which cerium ions are to be washed out are treated with a mineral acid solution of ascorbic acid; preferentially the concentration of ascorbic acid is 0.01 to 2 mol/l, particularly preferably 0.1 to 0.5 mol/l, that of the mineral acid 0.01 to 2 mol/l, particularly preferably 0.1 to 0.5 mol/l. Preferred mineral acids are perchloric acid and in particular sulfuric acid. The washing process is typically carried out at 4xc2x0 C. to 80xc2x0 C., preferentially at 15xc2x0 C. to 30xc2x0 C., according to customary procedures, for example using a suction filter or by sedimentation and decantation. Washing is typically carried out with 3 to 10, usually 4 to 5, bed volumes of the solution.
The concentrations of the cerium salts are determined by means of optical emission spectrometry using a commercially available ICP spectrometer. The proportion by weight of cerium is measured on the basis of the calibration using cerium salts and customarily indicated in ppm (parts per million) as the percentage by weight of cerium based on the weight of the dried separating material. The separating material is dried for the analysis according to customary procedures, such that it has a water content determined according to Karl-Fischer of less than 0.1 percent by weight. Details of the cerium determination are found in Example 1. Using the process according to the invention, separating materials are obtained which contain between 1 and 10 ppm, customarily below 1 ppm, of cerium.
Even without further details, it is to be assumed that a person skilled in the art can utilize the above description to the widest possible extent. The preferred embodiments and examples are therefore only to be interpreted as descriptive, but in no way as limiting disclosure in any manner.
The complete disclosure of all applications, patents and publications mentioned above and below, in particular that of the corresponding application DE 198 37 020.2, filed on Aug. 14, 1998, are inserted into this application by way of reference.